Local hyperthermia therapy for cancer can produce selective heating of solid tumors on the basis of known physical laws. The goal of therapy is to achieve temperature elevations in the tumor for a period of time adequate to produce tumor necrosis without damaging nearby normal tissues. As we have shown both experimentally and theoretically, a low rate of blood flow in the tumor or a rapid rate of blood flow in adjacent normal tissues can enhance selective tumor heating. This proposal seeks support for a controlled clinical trial of vasodilator drugs, which act selectively on normal vessels to promote blood cooling of normal tissues, as an adjunct to local heat therapy of spontaneously arising tumors in dogs. Using a factorial, completely randomized experimental design we will correlate success of therapy with the histologic type, size, and location of the canine tumors, such that recommendations for transferring the therapy to human medicine can be made.